The use of robotics to perform welding operations is well known. Typically, robotics are used to increase production and/or to reduce human exposure to harsh and/or undesirable working conditions. One such environment is the welding of large door frames. Such door frames are difficult to assemble due to their overall size and weight. Many metal door frames are over six feet long and over two feet wide, thereby creating difficulties in loading the door components properly for welding and unloading the welded door frame without damaging the door frame. A standard metal door frame includes several components, such as longitudinal rails and transverse rails. These longitudinal rails are normally over six feet long while the transverse rails are normally over two feet long. When the door components are welded together, a complete door frame is produced.
The quality of the welded door frame is influenced by several factors. These factors include the accuracy of the position of the door frame components relative to one another, the ability of the welding head to be properly positioned with respect to the door frame components, and the manner by which the welded door frame is removed from the work area. If the door components are not properly positioned relative to one another, the welded door frame will have dimensional quality problems. If the welded door frame is not carefully and properly removed from the welding platform, the door frame can be bent or otherwise damaged. Furthermore, if the welding head of the welder is not properly positioned with respect to the door frame components during the welding, the integrity of the welded joint may be defective compromised.
One of the problems associated with the use of a robotic welder to position the weld head on the door frame components during welding is that the robot is typically "blind." As a result, the robotic welder is unable to ascertain the location of the door components on the work surface. Consequently, the robotic welder is completely dependent on the door frame components being accurately and consistently positioned on the work surface during the welding process so that a quality door frame is produced.
Another problem associated with the use of robotic welders is that robotic welders are costly, thereby making effective utilization of such robotic welders necessary in order to justify the cost of using such a welder. Therefore, wasteful idle time of the robotic welder should be minimized. One of the primary sources of idle time is attributable to manual tasks performed by an operator during the welding process (i.e. loading and unloading the door components). Typically, a robotic welder is able to weld the door frame components within the time necessary for an operator to load the door frame components onto the work surface. However, significant idle time results when the operator loads the door components onto the work surface and unloads the welded door frame from the work surface after the robotic welder has welded the door components together. Such idle time reduces production rates and does not optimize the use of the robotic welder.
Several attempts have been made to reduce the problems associated with the idle time of the robotic welder. These past attempts involved the design of welding systems that allow an operator to unload the welded door assembly and/or load the door components onto the work surface while the robotic welder is welding the door frame component. These designs reduce idle time by having the robotic welder weld the door frame components together while the operator spends time loading the door components onto the work surface and/or removing the welded door from the work surface.
One type of welding system which utilizes an improved welding system utilizes a rotary work table which work table is rotatable about a vertical axis. This configuration allows for multiple work stations to be positioned about the rotary work table. The work table includes two work surfaces and is mechanically rotated to move the door components from the operator's work station to the robotic welder work station and then to move the welded door frame assembly back to the operator's work station. The rotating work table allows the operator to unload a welded door assembly and load the door components onto the work table while the robotic welder is welding the previously loaded door components. Although this welding system reduces idle time of the robotic welder, the welding system has several disadvantages. One disadvantage is the size of the work table needed to rotate large workpieces. Door frame components which must lay flat on the work table require the work table to be over six feet tall or six feet wide to accommodate the door frame. The difficulty in loading the door frame components onto the work table results additional idle time of the robotic welder. The manipulation of the large door components onto the work surface requires extensive bending and reaching movements by the operator to position the door components onto the work surface. The difficulty in removing the welded door frame from the work table also results in additional idle time of the robotic welder and can result in damage to the door frame. Furthermore, the work table configuration requires one work station to be used both as an unloading station and as a loading station. The time required to unload a welded door frame assembly and then to load the door components onto the work table results in significant idle time of the robotic welder. Another disadvantage of this welding system is that the door components are welded in a vertical position. In many welding applications, the vertical welding position does not create the optimum type of weld bead on the welded components. The inability of the welding system to weld at various welding positions limits the versatility of the welding system.
Another type of welding system which reduces idle time is a welding system which incorporates the use of multiple independent work tables. These work tables are generally stationary and require the robotic welder and the operator to move back and forth between the independent work tables. Typically, there are two independent work tables located on opposite sides of the robotic welder. The robotic welder performs the welding operation on one work table while the operator unloads a welded door frame and subsequently loads the door frame components on the second work table. Once the door components are loaded onto the second work table, the robotic welder moves to the second work table to begin welding the door components and the operator moves to the first work support table to remove the welded door frame and to then load the door components for later welding. These operations are repeated requiring both the operator and the robotic welder to move from one work table to another. Although this welding system does reduce the idle time of the robotic welder, the welding system has many disadvantages. One of the disadvantages associated with this welding system is that the operator must continuously move between the two work stations during the welding process. This movement between the two work tables is time consuming, results in increased operator fatigue which can thereby affect the quality and quantity of production. The movement of the robotic welder between two tables makes it difficult to shield the operator from "arc flash." Arc flash can cause irritation to the eyes over time. Furthermore, the time taken by the operator moving from one work table to another results in increased idle time of the robotic welder. To overcome this problem, two operators may be used; however, the use of more than one operator results in increased labor costs. Another disadvantage of this welding system is that the robotic welder must also move between the two work tables during the welding process. The movement of the robotic welder between two work tables results in additional idle time of the welder, and requires additional components to move the robotic welder between the two work tables thus resulting in a more complex and costly design. The multiple work tables also can result in reduced quality and consistency of the welded door frames. Because the robotic welder must move between two independent work tables, the positioning of the door components at the different work tables must be exact to ensure consistency and quality of the door frames. Therefore, the indexing mechanism for moving the robotic welder between the two work tables must be continuously serviced to ensure such accuracy. Such servicing results in down time thus reduced the quantity of welded door frames and also increases the cost of operating the robotic welder. In addition, the movement of the robotic welder between the two work tables also results in increased wear on the movement mechanisms of the robotic welder thereby increasing costs and reducing output efficiencies. Another disadvantage of the welding system is that the work surfaces are positioned parallel to the floor. The positions of the work surfaces can cause delays in loading the door components onto the work surface since the operator must walk around the work surface to position the components onto the work surface. This also causes operator fatigue due to excessive reaching over the surface to load the components. In addition, the position of the work surface only allows for down position welding thus limiting the versatility of the types of welds which can be formed.
In view of the deficiencies of prior robotic welding systems, there is a demand for a welding system which increases the ergonomics of the welding system without increasing idle time, which allows for welding at multiple angles, maintains the consistency of the welded product, and is relatively simple and cost effective to operate.